1. Field
Certain embodiments generally relate to communication systems, and for example, to device-to-device (D2D) communication integrated into a communications network, such as, but not limited to, long-term evolution (LTE) or long-term evolution advanced (LTE-A) cellular network specified by the 3rd Generation Partnership Project (3GPP).
2. Description of the Related Art
Two types of communication networks include cellular networks and ad-hoc networks. A cellular network is a radio network made up of one or more cells, where each cell is served by at least one centralized controller, such as a base station (BS), a Node B, or an evolved Node B (eNB). In a cellular network, a user equipment (UE) communicates with another UE via the centralized controller, where the centralized controller relays messages sent by a first UE to a second UE, and vice versa. In contrast, in an ad-hoc network, a UE directly communicates with another UE, without the need of a centralized controller. Utilizing a cellular network versus an ad-hoc network has its benefits and drawbacks. For example, utilizing a cellular network over an ad-hoc network provides the benefit of easy physical resource control and interference control. However, utilizing a cellular network over an ad-hoc network also provides the drawback of inefficient physical resource utilization. For instance, additional physical resources may be required in a cellular network when the two UEs are close to each other, as compared to an ad-hoc network.
A hybrid network utilizes both a cellular mode and a device-to-device (D2D) transmission mode. In a hybrid network, a UE may choose to communicate either via a cellular mode or a D2D transmission mode. As an example, a hybrid network may allow UEs to communicate either via a cellular mode (i.e. via a centralized controller) or via a D2D transmission mode where the UEs may establish a direct channel which may or may not be under the control of a centralized controller. The UE and/or its controlling network may make this selection depending on which mode provides better overall performance. Thus, a hybrid network may improve total system performance over a cellular network or an ad-hoc network. However, in order to utilize a hybrid network, issues related to physical resource sharing and interference situations may need to be addressed.
In addition, proximity services (ProSe)/D2D discovery and communication is one of the ongoing study items for 3GPP Release 12 (Rel-12) standardization (as well as Release 13 and beyond). D2D scenarios that are currently being studied in 3GPP include D2D in network coverage, out of network coverage, and partial network coverage scenarios. ProSe direct D2D LTE Rel-12 study item (SI) was approved at RAN #58 and concluded at RAN#63. As mentioned above, the two major topics to incorporate ProSe D2D in LTE specification are discovery and communication.